When did I ovulate?

Another app says I ovulated on CD18 but Glow says CD20. Could this be a slow rise and I did ovulate on CD18? LH surge on CD17, and heavy EWCM on CD17 and 18, but then more creamy and stretchy discharge on CD19/20. I have high basal LH (seeing Dr currently to check for PCOS) so not sure if surge is accurate, and I typically have a lot of stretchy discharge all throughout cycle.